Attempts have been made previously to improve the life of the hinges of book-style cassette albums. For example, U.S. Pat. No. 4,407,410 describes an album having a spine which is curved so as to bow outwardly providing a rounded back. No hinges are formed at the edges of the spine. The rounded backs, however, are thought by many to present a poor appearance.
One objective of the present invention is to provide a tailored, straight back; i.e., a flat, neat looking spine having well defined corners where the edges of the spine intersect the front and rear album covers. This configuration presents a clean, tailored look with good visual appeal and an appearance more similar to that of an ordinary book. A flat spine also presents graphic material more clearly than a round back which distorts the image.
Other prior designs such as those described in U.S. Pat. Nos. 4,641,750; 4,718,550 and 4,784,264 provide a flat spine having a good appearance but the hinges, while usually satisfactory, sometimes crack or split. Occasionally, there are complaints about the hinges breaking, particularly if the album is subject to heavy use. In these albums the hinge is formed by pressure exerted against the sheets with a pair of vertically heated bars. When the bars are pressed together on opposite sides of the plastic sheet material, two laterally spaced apart thermally heated hinge rules are formed which define narrow depressions or longitudinal notches in the sheet material. Each spine rule thus comprises a narrow groove or recess of reduced thickness with a raised border of greater thickness on each side as shown in FIG. 5 of U.S. Pat. No. 4,641,750. Such spine rules form a weak point where breakage can occur.
Another difficulty with some of the prior albums is their tendency to pop open prematurely because of residual stresses in the hinges which act as springs tending to open the album. Moreover, the process used in preparing spine rules previously employed also has a tendency to limit production rates.
The prior application Ser. No. 436,453 and other albums of that kind, while very good, have a weak point; they tend to buckle or collapse when a force is applied to the album which presses the covers toward one another. Another problem in prior albums is the tendency for the spine to bow outwardly so as to destroy the clean lines and the desired flatness in the spine area.
U.S. Pat. No. 4,635,797 describes a package having two separate trays which are spaced apart from one another in the spine area. The vinyl coated paperboard cover stock material is provided with a pair of embossments to define hinges. Both trays have to be formed, handled and sealed to the cover stock material separately, tending to slow production. It is an object of the present invention to provide an album suited for rapid mass production while providing the strength advantage of having a strong, relatively stiff and durable tray stock material extending through the hinges in the spine area. It is also an object to provide the hinges in the stiff and durable tray material rather than in the relatively soft cover stock material and to conform the soft cover layer over the hinges of the inner tray sheet to provide smooth tailored corners at the fold lines between the spine and the covers of the album.
In view of these deficiencies, it is a major objective of the invention to find a way to provide durable, crack resistant hinges in a strong inner tray sheet layer. It is another object to provide an album with a soft and supple outer cover stock layer conforming to the relatively firm inner supporting hinges so as to provide square corners along each edge of the spine. Another object is to provide better flexibility of the hinges with less residual stress in the hinge area when the album is in the closed position. A further object is to find a way to increase production rates, thereby lowering manufacturing costs. A further object is to hold cardboard inserts in place without the provision of a spine rule. Another object is to strengthen and rigidify the spine and keep the spine flat without the necessity of using a piece of cardboard for spine reinforcement.
These and other more detailed and specific objects of the present invention will be apparent in view of the following description setting forth by way of example but one of the various forms of the invention that will be apparent to those skilled in the art once the principles described herein are understood.